Cat C-12 Water valve info

Follow the heater hoses from the cab. There might be 4 valves, 2 from cab, 2 from sleeper. The sleeper I shut off from spring till fall. I leave the cab valves open an 1/8th turn in case I hit fog or something. They are shut all the way off right now though, due to the abundance of triple digit heat. Closer to fall I open them an 1/4 turn.

 

Either valve coming from the right side of the engine up to the heater core will stop the water flow through it. just make sure that they go to the heater core up through the firewall and not something else like to a APU unit or somthing. but either one or both will keep the heatercore from getting hot water flowing through it. It sounds like the heater valve or the actuator door isn't shutting off but i can't rember which one it has on that year model if it still has the water valve under the fire wall on the pass side than either the valve is stuck open or the actuator that controlls it is bad. If thre isn't anthing there than it has a actuator under the dash kinda in the middle part that controls a door that shuts the passage way off to the heatercore in the HVAC unit and its probably went bad on you. The one under the hood on the pass side is much easier to change and fixx.